The present invention relates to processes and apparatus for recovering dichlorohydrins from a mixture comprising the same such as the effluent generated by a process for converting multihydroxylated-aliphatic hydrocarbon compound(s) and/or ester(s) thereof to chlorohydrins.
Dichlorohydrins are useful in preparing epoxides such as epichlorohydrin. Epichlorohydrin is a widely used precursor to epoxy resins. Epichlorohydrin is a monomer which is commonly used for the alkylation of para-bisphenol A. The resultant diepoxide, either as a free monomer or oligomeric diepoxide, may be advanced to high molecular weight resins which are used for example in electrical laminates, can coatings, automotive topcoats and clearcoats.
Glycerin is considered to be a low-cost, renewable feedstock that is a co-product of the biodiesel process for making fuel. It is known that other renewable feedstocks such as fructose, glucose and sorbitol can be hydrogenolized to produce mixtures of vicinal diols and triols, such as glycerin, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and the like. With abundant and low cost glycerin or mixed glycols, economically attractive processes for recovering dichlorohydrins from effluents produced by the above processes are desired.
A process is known for the conversion of glycerol (also referred to herein as “glycerin”) to mixtures of dichloropropanols, compounds I and II, as shown in Scheme 1 below. The reaction is carried out in the presence of anhydrous HCl and an acetic acid (HOAc) catalyst with water removal. Compounds I and II can then be converted to epichlorohydrin via treatment with caustic or lime.

Various processes using the above chemistry in Scheme 1 have been reported in the prior art. For example, epichlorohydrin can be prepared by reacting a dichloropropanol such as 2,3-dichloro-1-propanol or 1,3-dichloro-2-propanol with base. Dichloropropanol, in turn, can be prepared at atmospheric pressure from glycerol, anhydrous hydrochloric acid, and an acid catalyst. A large excess of hydrogen chloride (HCl) was recommended to promote the azeotropic removal of water that is formed during the course of the reaction.
WO 2006/020234 A1 describes a process for conversion of a glycerol or an ester or a mixture thereof to a chlorohydrin, comprising the step of contacting a multihydroxylated-aliphatic hydrocarbon compound, an ester of a multihydroxylated-aliphatic hydrocarbon, or a mixture thereof with a source of a superatmospheric partial pressure of hydrogen chloride to produce chlorohydrins, esters of chlorohydrins, or mixtures thereof in the presence of an organic acid catalyst. This process is referred to herein as a “dry process” because the process uses dry hydrogen chloride and the source of water in the process is essentially only the water generated in the reaction as a co-product. In the dry process, azeotropic removal of water, via a large excess of hydrogen chloride, is not required to obtain high chlorohydrins yield. WO 2006/20234 A1 further teaches that separation of the product stream from the reaction mixture may be carried out with a suitable separation vessel such as one or more distillation columns, flash vessels, extraction columns or adsorption columns. WO 2006/020234 A1 does not describe a specific distillation process and apparatus for efficient recovery of dichlorohydrins or a method to minimize formation of heavy byproducts.
WO 2005/021476 A1 describes a process using atmospheric partial pressure of hydrogen chloride, acetic acid as the catalyst, and a cascade of loops, preferably three loops, each loop consisting of a reactor and a distillation column in which water of reaction, residual hydrogen chloride and dichloropropanol are removed from the reaction effluent. This process for distillation requiring a cascade of reactor/distillation loops is very expensive as it requires several reactors/columns loops in the process. WO 2005/021476 A1 also does not describe a specific distillation method or a method to minimize formation of heavy byproducts. Furthermore, valuable acetic acid is lost with the distillate during distillation, resulting in a large rate of acetic acid consumption in the process, making the process expensive to operate.
EP 1 752 435 A1 (also published as WO 2005/054167) as well as EP 1 762 556 A1 disclose other processes for producing chlorohydrins by reaction between glycerol and aqueous hydrogen chloride to produce dichlorohydrins, under atmospheric conditions. This process is referred to herein as a “wet process” as it, not only produces water from the reaction, but also adds a large amount of water into the process via the aqueous hydrogen chloride reactant. This wet process requires three separation columns, a distillation column for distillation of the reactor's gas phase to remove the large excess of water from the reaction medium while keeping hydrogen chloride in the process, a stripper column to strip water and hydrogen chloride from the reactor's liquid phase and yet another distillation or a stripping column for recovering dichloropropanol from the liquid phase exiting the stripper. Some dichloropropanol is removed from the reaction medium in the first and the second separation columns because of existence of a pseudoazeotrope among dichloropropanol, water and hydrogen chloride. The main fraction of dichloropropanol is collected from the top of the distillation or stripping column, third separation column. This process has a very high energy consumption because of the need to evaporate a large amount of water from the process. This process is unsuitable for efficiently recovering dichlorohydrins from a reaction effluent of a dry process. Similarly, adding substantial amounts of water to the dichloropropanol adds substantively to the wastewater treatment requirements of downstream operations.
CN 101007751A describes another process that combines wet and dry processes with two reactor in series, in which tubular reactor is used as the first reactor and foaming-tank reactor is used as the second reactor. Aqueous hydrogen chloride, glycerin, carboxylic acid catalyst are mixed and fed to the first reactor and gaseous hydrogen chloride is fed to the second reactor. Inert impurities are added to the gaseous hydrogen chloride feed in order to improve the efficiency of stripping water from the reaction mixture in the foaming-tank reactor. The azeotropic composition of generated water, dichloropropanol and hydrogen chloride and part of the catalyst are evaporated from the top of foaming-tank reactor. The liquid bottom product of the foaming-tank reactor enters to a rectifying tower for separation. The dichloropropanol product is obtained from the rectifying tower distillates and the tower bottom residue is recycled to the foaming-tank reactor. This process shows lower hydrogen chloride conversion than that of the dry process, generates excess water where azeotropic removal of water is required, which implies larger process equipment than that of the dry process. CN 101007751A also does not describe specific distillation method to minimize formation of heavy byproducts.
U.S. Provisional Patent Application Ser. No. 60/923,108 entitled “MULTI-STAGE PROCESS AND APPARATUS FOR RECOVERING DICHLOROHYDRINS” filed Apr. 12, 2007 by Tirtowidjojo et al. describes a dual column separation process for separating dichlorohydrins from the effluent streams of reactors, but uses a stripping agent to effect the evaporation of the dichlorohydrin (dichloropropanol) from the mixture. This stripping agent then requires subsequent separation unit operations to become sufficiently cleaned to either recycle as a stripping agent or to discharge to the environment. These subsequent separation unit operations are typically additional distillation/fractionation unit operations that significantly increase the energy utilization of the overall process.
Opportunities remain to further improve recovery of dichlorohydrins from a dichlorohydrins comprising stream, in a form that can be used in subsequent conversions, such as the conversion to epichlorohydrin, and reduce energy utilization while maintaining the quality of dichlorohydrin product produced and not increasing the amount of undesired byproducts formed.